SPE Western Regional Meeting,
21-23 March 2012,
Bakersfield, California, USA
This paper presents the first semi-analytic solution of two-phase two-component
compressible flow in permeable media using method of characteristics (MOC).
Analytical solutions are important as numerical simulations do not yield
explicit expressions in terms of the model parameters. However, the previously
developed MOC solutions rely on the incompressible fluid and rock assumptions
that are rarely met in practice Furthermore, numerical simulations that provide
the most comprehensive solutions to multiphase flow problems are
computationally intensive. In this study, the method of characteristics (MOC)
solution of the overall mass conservation equation of CO2 in two-phase
two-component flow through permeable media is derived with no restriction on
the compressibility of fluids and the rock.
A simulation approach is used to verify the derived analytical solutions. The
simulation models consist of a vertical injection well and a producer located
at the ends of a one-dimensional (1D) grid. The pace at which specific gas
saturations propagate along the permeable medium are compared with the gas
saturation profiles obtained when no compressibility is involved.
The results suggest that the velocity of a wave, which is associated with the
transport of a certain mass of CO2 along the permeable medium, is a function of
the gas saturation, compressibility of the rock and fluids, and the pressure
gradient. The results reveal that the wave velocity will only be a function of
the gas saturation and pressure gradient if the compressibility of the rock is
negligible compared to that of CO2. Hence, the waves’ velocity will only depend
on saturation, as is for an incompressible flow system, when changes in
pressure gradient are minimal.
Thus, this paper explains how fast a compressible CO2 plume will travel along
the aquifers length. In practice, the fate of the injected CO2 plume is
essential to determine the storage capacity of aquifers and to evaluate the
risk associated with the CO2 sequestration projects.
Despite extensive research on analytical modeling of CO2 sequestration in
saline aquifers (Szulczewski et al., 2009; Juanes et al., 2010; Ghanbarnezhad
et al., 2011), the gas always has been considered as an incompressible fluid.
The method of characteristics (MOC) solution of the overall composition balance
equation of CO2 is derived for one-dimensional (1D) two-phase two-component
flow in the presence of compressibility. In the following study, the
incompressible assumption is relaxed and compressibility is represented by